Piezoelectric oscillators are required to output a stable frequency without being influenced by a change in ambient temperature. Therefore, as described, for example, in Japanese Unexamined Patent Application Publication No. 2013-211752 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2010-183324, the output frequency of a piezoelectric resonator is stabilized by performing temperature control to keep the temperature of the piezoelectric resonator at a desirable temperature by using a heater or the like. For example, in Patent Document 1, in order to suppress dissipation of heat from the inside to the outside of a recess that accommodates a piezoelectric resonator, the recess is hermetically sealed with a three-layer structure that is composed of a first metal plate, a resin member, and a second metal plate (see paragraph 0029 and FIG. 3 of Patent Document 1). Patent Document 1 also describes a structure in which a space, instead of the resin member, is provided between the first metal plate and the second metal plate.
However, with these structures, because the second metal plate, which serves as a lid, is joined to the first metal plate, sealability may be impaired due to warping or deforming of some members due to heat, and thus it may not be possible to achieve a sufficient heat insulating effect.
The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a piezoelectric oscillator and piezoelectric oscillation device that can improve sealability and heat insulation ability for a piezoelectric resonator.